Macroscopic membranes play an important role in many biological processes at both the cellular and organismic level. In addition, membranes are used in a number of medical, research, and industrial applications. Physiologically compatible membranes would be especially valuable for biomedical products. At present, the self-assembly of peptides into macroscopic membranes has not been reported.
The invention relates to the discovery that a new class of biomaterials derived from peptides related to the yeast DNA binding protein zuotin. The oligopeptides are generally stable in aqueous solutions and self-assemble into large, extremely stable macroscopic structures or matrices when exposed to physiological levels of salt. The biomaterials are visible to the naked eye when stained with a dye, Congo Red, and can form sheet-like or fibril structures which have high tensile strength. These materials are substantially resistant to change in pH, heat, and enzymatic proteolysis. The biomaterials can have a fibrous microstructure with small pores as revealed by electron microscopy.
A-small peptide termed EAK16 (AEAEAKAKAEAEAKAK, aa 310-325 of SEQ ID NO: 2) was discovered serendipitously to self-assemble into stable macroscopic membranes and filaments in the presence of millimolar concentrations of salt. This invention relates to the self-assembly of peptides into stable macroscopic membranes and filaments. Peptides which form membranes are characterized as being amphiphilic, e.g., having alternating hydrophobic and hydrophilic amino acid residues; greater than 12 amino acids, and preferably at least 16 amino acids; complementary and structurally compatible. Complementary refers to the ability of the peptides to interact through ionized pairs and/or hydrogen bonds which form between their hydrophilic side-chains, and structurally compatible refers to the ability of complementary peptides to maintain a constant distance between their peptide backbones. Peptides having these properties participate in intermolecular interactions which result in the formation and stabilization of xcex2-sheets at the secondary structure level and interwoven filaments at the tertiary structure level.
Both homogeneous and heterogeneous mixtures of peptides characterized by the above-mentioned properties can form stable macroscopic membranes and filaments.
Peptides which are self-complementary and self-compatible can form membranes in a homogeneous mixture. Heterogeneous peptides, including those which cannot form membranes in homogeneous solutions, which are complementary and/or structurally compatible with each other can also self-assemble into macroscopic membranes and filaments.
Peptides which can self-assemble into macroscopic membranes and filaments, the conditions under which membrane and filament formation occurs, and methods for producing the membranes and filaments are described and included in this invention.
Macroscopic membranes and filaments formed of the peptide EAK16 have been found to be stable in aqueous solution, in serum, and in ethanol and are highly resistant to degradation by heat, alkaline and acidic pH (i.e., stable at pH 1.5-11), chemical denaturants (e.g., guanidine-HCl, urea and sodium dodecyl sulfate) and proteases in vitro (e.g., trypsin, xcex1-chymotrypsin, papain, protease K, and pronase). The membranes and filaments have also been found to be non-cytotoxic. The membranes are thin, transparent and resemble high density felt under high magnification. Being composed primarily of protein, the membranes and filaments can be digested and metabolized in animals and people. They have a simple composition, are permeable, and are easy and relatively inexpensive to produce in large quantities. The membranes and filaments can also be produced and stored in a sterile condition. Thus, the macroscopic membranes and filaments provided by this invention are potentially useful as biomaterial for medical products, as vehicles for slow-diffusion drug delivery, as separation matrices, for supporting in vitro cell attachment and growth, for supporting artificial tissue, e.g., for in vivo use, and for other uses requiring permeable and water-insoluble material.
Furthermore, the salt-induced assembly of the peptides into insoluble and protease-resistant protein filaments with a xcex2-sheet secondary structure is similar in some respects to the formation of the neurofibrillary filaments and amyloid plaques associated with Alzheimer""s disease and the formation of scrapie prion protein filaments liver cirrhosis, kidney amyloidosis, and other protein confirmational diseases. The formation of the macroscopic membranes and filaments can, therefore, be useful as a model system, e.g. to study these pathological processes. For example, such a model system can be used to identify drugs which inhibit filament formation and are thus useful for treating Alzheimer""s disease and scrapie infection.
Peptide EAK16 was derived from a region of a yeast protein, zuotin, which exhibits a high affinity for DNA in the left-handed Z conformation. Zuotin was identified by a gel shift assay for Z-DNA binding proteins developed by the Applicants. Applicants further cloned and sequenced the gene encoding zuotin. Characterization of zuotin revealed that the protein is a potential substrate for several protein kinases and identified a putative DNA-binding domain. This invention also includes all or biologically active portions of the zuotin protein and DNA encoding zuotin.